Question

I am trying to find a function to match two data frames of different lengths on one common column only, and create a different column which specifies if it found a match or not.
So, for example,
df1 is:

Name Position location
francesca A 75
cristina B 36

And df2 is:

location Country
75 UK
56 Austria

And I would like to match on “Location” and the output to be something like:

Name Position Location Match
francesca A 75 1
cristina B 36 0

I have tried with the function match or with:

subset(df1, location %in% df2)

But it does not work.

Could you please help me figure out how to do this?

Answer 1

Try:

df1$match <- match(df1$location, df2$location, nomatch=0)

This will add a column to df1 indicating which row in df2 matches it (considering only location as you specified). If there are no matches, zero will be returned, so you get:

> df1
       Name Position location match 
1 francesca        A       75     1
2  cristina        B       36     0

One caution: if there are multiple matches in the second table, you’d want to use a different approach as this method only returns the first match. I assume these are unique because of the way you specified your question, so this should not be an issue.